Conventionally, there are heat supply systems that allow heat generated by a heat source device to be used for hot water supply or indoor heating. For example, in a heat supply system described in Patent Document 1 (JP 2013-104596A), warm water in which heat generated by heat source devices, namely a heat pump (2) and an external heat source (3), has been recovered is supplied to a hot water storage tank (4) and an indoor heating device (5), while flowing through a water circuit (25) and warm water circuits (30A and 30B). When this heat supply system is installed in a building such as a house, it is also necessary to install the water circuit (25) and the warm water circuits (30A and 30B) indoors. Therefore, such a heat supply system is usually installed together with building construction.